Various types of positioning apparatus are known on the market. Specifically, electrically actuable cylinders are known. One typical device of this type is a Model 15D manufactured by Industrial Devices Corporation of Novato, California, U.S.A.. This electric cylinder includes fixed outer housing, a fixed screw thread rotatably mounted in the housing and a translatable riding member which translates axially in response to rotation of the screw thread. A piston extension member is mounted for movement together with the translatable riding member.
The above-described device is lubricated with grease, and cannot, as a matter of practicality, be filled with oil because too many seals would be required and no provision was made for accomodating the change in interior volume due to differing displacements of the piston.
Electrically acutuable cylinders of the type described hereinabove are relatively expensive due to their complexity. Due to the fact that they are lubricated with grease, having relatively poor heat distribution characteristics as compared with oil, their mechanical efficiency and operating lifetime are relatively low.
X-Y tables of various designs are also known and typically comprise a plurality of screw drives arranged along perpendicular axes. Due to the requirement for independent X, Y motion, part of the drives, including their power sources, are required to move. As a result, X-Y tables are generally complex and expensive.
Robots of various designs are known. Typically, prior art robots comprise extensible members which are arranged for selectable extension along relatively perpendicular axes.